Gun synchronizing apparatus



July 17, 1951 s, J, BARR GUN SYNCHRONIZING APPARATUS 3 Sheets-Sheet 1 Filed March 4, 1947 IF" If]- R M w W n W j T: J 4 w A. m .v n: .E 5 a 0 J m w 7 7 6 NH 2 4 5 2 a a m A] W. H .m nw

6 O 2 d M 2 2 WWW-WW? July 17, 1951 5, J, BARR GUN SYNCHRONIZING APPARATUS Filed March 4, 1947 5 Sheets-Sheet 2 I 20 I H 1" 1' :70 g0 go I Z9 grvua/wm .70 I 5x55111011? J- Barr July 17, 1951 s, J, BARR GUN SYNCHRONIZING APPARATUS S Sheets-Sheet 5 Filed March 4, 1947 San man? J. IElar-r' Patented July 17, 1951 'UITED STATES OFFICE GUN SYN CHBONIZING APPARATUS Seymour J. Barr, Aberdeen, Md.

Application March 4, 13-17, Serial No. 732,367

(Granted under the act of March 3, 1883, as amended April 30, 1928; 37!) Q. G. 757) 9 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

The present invention relates to an apparatus and method for synchronizing the firing of guns.

In certain types of gun mounts such as antiaircraft mounts, for example, it is customary to install a plurality of; guns on one mount or carriage to be elevated or traversed as one. In such multiple-gun installations it is highly desirable to fire the guns simultaneously because the individual guns are located oiT the center of rotation of the mount and in non-synchronous fire the guns will tend to jerk or whip about the center of rotation causing instability of the mount. Such instability is particularly undesirable for antiaircraft firing as it greatly handicaps the tracking of moving targets. Synchronizing devices of the prior art have not approached completely synchronous fire because they have not overcome the many variables which affect synchronized fire.

An important object of the present invention is to provide a gun synchronizing apparatus and method which will overcome the variables affecting such fire and result in substantially completely synchronous fire.

Another object of the present invention is the provision of an apparatus of this character which may be readily applied to guns as an attachment or as an integral part of the installation during manufacture.

A further object of the invention is to provide a device of the above mentioned character which is of simple construction, inexpensive to manufacture and install, and positive and efficient in operation.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the accompanying drawings, which form a part of this specification, and wherein like charactors of reference denote like parts throughout,

Figure l is a side elevation of a twin gun mount having the present invention applied thereto;

Figure 2 is an enlarged fragmentary side elevation thereof, showing the side cover of the breech of the near gun open, for purposes of illustration;

Figure 3 is a fragmentary vertical section taken upon a plane indicated by the line 3-3, Figure 1;

Figure 4 is a fragmentary top plan .view of the breech portions of the twin guns, parts being shown in section;

Figure 5 is a diagrammatic view of the synchronizing circuits,

Figure 6 is a detail side elevation of a portion of the trigger mechanism of one of the guns set for single fire action and illustrating the circuit connections to the trigger,

Fig. 7 is a detail perspective view showing the breechblock in substantially lowered or open position and the firing pin in cocked position.

Fig. 8 is a detail perspective view showing the manner in which movement of the .breechblock into closed positionoperates to release the firing pin for firing movement, and

Fig. 9- is a detail perspective view corresponding ,to Fig. '7 butshowing the firing pin in firin position and the breechblockclosed.

In the drawings, wherein for the purpose of illustration is shown a preferred embodiment of the invention, the numeral l0. designates one gun and the numeral ll the other gun in a twin mount. The guns illustrated are 40 mm. guns designed for automatic .fire as well as single fire but the invention may obviously be employed with other type guns and for any number of guns arranged on the same mount or in the same installation. The method of mounting the guns is not material to this invention, but as is usual inguns of this type, they are mounted for traverse and elevation as a unit. The 40 mm. guns illustrated in the drawings are of the usual construction and include a breech casing 12 supported in the mount by suitable trunnions such as shown at L3 in Figs. 1 and 2. The recoiling parts of the gun slide within the breech casing and include a breech ring M detachably connected tothebarrel of the gun and having an opening disposedthereinto receive a breechblock i5 moved downwardly within the breechblock from closed to open position by right and left inner cranks 5| and 52, Fig. 8, splined to a crank shaft 50. These cranks 50 and 5| have lugson their inneroheeks which engage cam slots formed in the respective sides of the breechblock so that rotation of the shaft counterclockwise as viewed in Fig. 7, lowers the breechblock. Such rotation of crank shaft 50 is efiected by an outer crank It splined to the shaft and having a roller 21 journaled on its outer end. As the barrel and breech assembly recoil, roller 2|, in moving rear! wardly with the assembly, is engaged by a sta-,

the block becomes fully lowered, extractors,

shown, engage projections in the breechblock and act to hold it in lowered position.

A firing pin 53 is mounted within a bore in breechblock l5 for reciprocation from the cooked position shown in Fig. 7 to the firing position shown in Fig. 9. The firing pin is urged forwardly to firing position by a spring 54 extending between the pin and an abutment 55. A cocking shaft 55 which is journaled in a transverse bore near the front and bottom of the breechblock, has an angled inner cocking lever 51 fixed thereto and forming a firing-pin-en" gaging arm 51a. and a check-plunger-engaging arm 51b. The left end of shaft 56 has an outer bent cocking lever 58 fixed thereto. Lever 58 is mounted near a horizontal groove on the left side of the breechblock.

Check plunger 59 is a shaft having two diiferent diameters to form a shoulder therebetween. This plunger is mounted for axial sliding movement only in a transverse bore through the lower central portion of the breechblock. The shaft projects from the breechblock at both of its ends and is adapted to be shifted axially in each direction by a corresponding one of inner cranks 5| and 52. The check plunger 59 has a notch 59a in its portion of larger diameter which, when the parts are positioned as in Fig. '7, permits the end of arm 51b to pass the plunger. A spring 60 surrounds the reduced portion of check plunger 59 and acts continuously to urge the plunger to the right as the parts are viewed in Fig. 8.

Shifting of check plunger 59 in each direction of axial movement is effected by lugs or cam surfaces formed on the inner cheeks of cranks Hand 52. One such surface is identified at 5|a on crank 5|, Fig. 8. Thus, as shaft 50 is rotated in response to recoil, to thereby rotate cranks 5| and 52 in lowering of the breechblock, a lug on crank 52 engages outer cocking lever 58, and rotates shaft 56 and lever 51 clockwise as viewed in Fig. 7. This causes the endv of arm 51a of inner cocking lever 51 to engage the for wardly-facing shoulder 53a of firing pin 53 and forces the pin rearwardly into cocked position. As the breechblock moves into fully lowered position, crank 5| moves clear of the adjacent end of check plunger 59 while, at the same time a' cam surface (not shown) on the inner cheek of crank 52, engages the other end of the plunger and, assisted by spring 50, positively forces the plunger toward crank 5|. Since arm 5'") of the inner cocking lever is at this time fully lowered and the firing pin fully cooked, a side of notch 59a moves into an arcuate recess 510 in the end of arm 51b and thus acts to lock the cooking lever and firing pin in cocked position, that is, the position shown in Fig. 1. As the barrel and breech assembly return to battery the parts are held in the position shown in this figure so that,

during this time, crank l6 and roller 2| move in translation only. As the breech assembly nears battery position, a fresh cartridge is automatically rammed into the breech chamber. Justprior to the time the round is fully seated, the rim of the cartridge engages the extractors and forces them out of holding engagement with the breechblock. The latter now rises rapidly under urge of its spring 43 causing clockwise rotation of shaft 50 and cranks IB, 5| and 52. A small fraction of a second after the breechblock moves into fully closed position, projection 5|a on the inner cheek of crank 5| engages the adjacent end of plunger 59 and forces it to the left as viewed in Fig. 8 untilnotch 59a is aligned with the end of arm 51b of the cooking lever. This releases the firing pin for forward firing movement under the urge of its compressed spring 5 It will thus be seen that crank l6 and roller 2| are held lowered during counterrecoil until the breechblock is freed for upward movement by the action of the cartridge in forcing the extractors out of holding engagement with the breechblock.

The mm. automatic gun thus far described is of known construction and forms no part of the present invention. It is illustrated and described simply to develop the coaction between the gun and the novel mechanism to be described, and to comply with the requirements of the patent statutes. It is important to note the action of the breechblock and the movement of crank it and its rollers 2! just described.

From the foregoing description it will be noted that when the gun is in automatic fire, the firing mechanism is operated by and in response to movement of the breechblock into fully closed position. In fact firing takes place about .015

second after the breechblock moves into fully closed position. It is therefore evident that the important variables affecting synchronous fire of twin guns are found in the ramming operations which release the breechblocks, and in the tensioning of the breechblock closing springs. Any delay in such ramming operation, due to differences in the smoothness of the paths of the rounds, or in the rammer springs, or in the viscosity of the grease in the rammer springs, or

to other causes, will delay tripping of the extractors which release the breechblocks and therefore will prevent attainment of any close approach to synchronous fire. The present in vention overcomes these difficulties by synchronizing the final closing movement of the breechblock after the ramming operation so as to attain or very closely approach completely synchronous fire.

In accordance with the present invention the breech casing side cover N3 of each gun is provided on its outer face with a solenoid l9 riveted, I

bolted or otherwise secured to the side cover and having a spring pressed plunger or detent 20 extending through an opening in the side cover into the cam groove I! and in the path of the roller 2| carried by the outer crank I6 fixed on crankshaft 50, Figure 3, for engagement with the cam groove. The side cover I8 is pivoted to the breech casing l2, being shown in closed position in Figures 1 and 3 and in open position in Figure 2. Preferably a recess 22 is provided in the breech ring M to movement of the plunger 20 under pressure exerted by the roller 2| and crank arm I6 as the closing spring rotates the crank shaft in closing the breech.

Each breech casing side cover has a switch 23 mounted thereon in spaced relation with the solenoid l9 and preferably below the solenoid in vertical alignment therewith as shown. in Figures 1, 2 and 3. The switch 23 may be of any suitable construction so as to be operated by a slight lateral movement of the plunger 20 under pressure from the crank roller 2|. One practical construction of the switch 23 is illustrated in Figures 3 and 5 but obviously other forms of switches may be used. In the form of switch illustrated in the drawings, the switch casing is of small size and is end-Efixechwithinthe switch casing andiextendingl verticallyupward througha slotczfi intth-easwitch; casing toe-position in proximiwrtoand-tprefera: my in physical contact w'ith: the plunger: 23: A contactpole 25is disposed withinthe switch casing in close spaced relation to' thespring arm; 24:: on' theside ofthe arm opposite tothe plunger. 20.;

the breechblock isreleased bythe exe tractors by the ramming of a cartridgeandi the closingspring rotates the crank shaft'to move the breeohblock toward closed position; roller 21 moVes-upWardIytQWard cam edge I 1- until it. engages the plunger 20. When roller=2l engages-be--- neathplunger 20, further'movement of 'thecranklll is prevented and the breechblock isthus pre---- vented-- from moving to fullyclosed position; Pressure of the roller 21 under tension of 'the closing spring displaces the-plunger to the right, Figure 2, the slight distance permitted by the size of recess 22, thereby-mm'ingspring arm 24'into contact with switch-pole-Zfii When the'plunger' 20 iswithdrawn from the path'of roller 21 by energization of solenoid i9, pressure on the plunger is released sothat the spring arm 2 is free=to move out of contact with switch pole 26.

A suitable electrical circuit for a two gun mount is illustrated inFigure 5, in which the twonormally open switches 23- are arrangedin a circuit 21 connected to a solenoid circuit 3E including the two'solenoids IS. A trigger switch 28 is disposed in. the solenoid circuit-30 to open and close the circuit while a battery or other sourceof electricalf current 29 supplies current to the circuits. A two" pole selector switch 3! is connected in circuit 30: to include switches2-3 and circuit 21 in the solenoid circuit when the switch is in its right hand position forsynchronousfire orto exclude theswitches 23 and circuit 21 by opening circuit 2l-when-theswitch is in its left hand position-for non-synchronous fire. It will beseenthat when selector-switch 3| is in synchronous fire position (right position in Figure 5) the circuit 2'! becomes a necessary part of the circuit 30- and in series therewith so that both switches 23 must be closed before the solenoids can be energized. However, when selector switch 3| is in non-synchronous fire position (left position in Figure 5) the solenoids [9 may be energized whether the switches 23 are open or closed, as the circuit 21 is electrically disconnected from the solenoid circuit 30.

The above described circuit arrangement is onethat can be effectively used, but obviously other suitable arrangements of circuits may be employed to obtain the desired result.

The trigger switch 28 may be of any suitable construction, but one form of such switch is illustrated in Figure 6'. The purpose of the trigger switch 28 is to close the solenoid circuit when the guns are fired non-synchronously so that 60';

the plungers 28 will be withdrawn out of the path of the rollers 21 when the breechblocks are closing, and also to deenergize the solenoidswhen the guns are not in operation. Each gun is provided with a trigger switch 28. mechanism is disposed on the side wall and floor of each breech casing i2 and is operated through trunnion I3 by a firing pedal (not shown) located on the gun carriage. The firing. lever fi on the first round;

6"; The trig er 3Bi isa1located in; the. U. -porti0n1 of the leven 32" and is pivoted. tothe wall of the-casing I2; The; firing lever pawl 37. is pivoted at: 38? between lugs: on. the rear of thelonger arm of:

the lever 32 and. is adapted toengage and be;

tripped by the firing; lever stop stud 39; When. the firing lever 32' ispulled forwardly in. the direction of the arrow, Figure 6, the pawl 31": rotates; the trigger about its axis against the Itensionof. the trigger spring Mlto fire the gun;

Automatic or single fire; action are alternatively selected by rotationof inner safety lever 4| which. is fi'xed. to the. inner end of'a shaft journaled in the. wall. of the breech. casing. and adjusted by.

1a.. second lever: (not: shown). on said shaft exteriorly; of. the casing. This second lever has a spring-loaded; plunger which permits it tobe locked in either of: three positions, by holes in: the. casing. wall; In single fire action, the, lever His manually adjustedso; that one of its shorter faces is opposite. the.' nose of trigger 3B. The trigger may then be rotated clockwise by pawl illrinfiresponsewtoapull on rod 3%, a distance such. thatipawl' 31- is-tripped by studtfi'tocompletely release the-trigger; For automatic fire, the lever M; is: manually'adjusted so that one of: itsilonger sides is; presented. to be contacted by the nose" of." trigger 38?. Ilhe lever thus limits rotation of the trigger and prevents the pawl from being tripped and cornpletely releasing the-trigger; By reference to: Figure 6': it will be seen that the trigger is connected in circuit 38; and a contact: 4251s: disposed'in a position to be engaged by the triggerito cl'ose the circuitt't whenever the lever 32: isiturnedbya pull on rod 351 counterclockwise rotation of lever is limited by engagement withlugs it, Figure 6:

In: operation, when the guns are set for automaticzfire, synchronization: comes into operation flee-rate of fire is set slightly below: the normal fireof the slower gun. If, for example, the left gun=rammed the round into the chamber ahead-of the right gun, the extractors will betripped?and-.the-breechblock will rise and rotate armv Iii. and its: roller 2'4 under influence of-fthe.closingzspring; Whenthe roller 2 l" engages the plunger: Zib the upward." movement of the breechblock is stopped just before it reachesfully. closed? position, and the block cannot complete its-closing. movement while the solenoid is deenergizeda Pressure of the roller 21 against the plunger." moves the plunger transversely a small distance which causes spring arm 26' to move into engagement with contact 26". However, as

55. the-:bizeechblooliof: the right gun has not closed;

The. trigger 5;

its: switch 23 is still open and both solenoids are deenergized. When; the block or the right gun. closes sufli'ciently for; its roller 2t to engage its plunger 20: and closeeitsswitch 23; both switches 23" will; berclosed andv both solenoids !91 will be energized, resulting in simultaneous withdrawal of." the two .plungers: 2.9: When the two 1 plungers are: withdrawm. the breeohblocks' of both guns, complete; their'closing movements simultaneously and. the rounds in both guns will: be fired simul-- taneously orso; nearly. simultaneously as not to impair; the, stabilityof: the mount. It; will: be understoomt-hat actual release. of the firing: pins to fire the guns is effected in the usual manner is substantially U-shaped and is pivoted in 7'0; by: movement ofthe breechblocks tofullyclosed bracket 33 fastened to the floor of the. breech. casing. The longer; upper arm of the lever; is pulled rearwardly by the firing. lever spring 34. and forwardly against tensionof; spring. 3.4:by the.

position. as shown, for; example,v in British. Patent: 3.98,(I8.l,,. complete accepted September; 7,, 1933; As; soon; as the guns fire; switches; 23: are opened. dueztozabsence ofapressure on. plungerszll, thereby.-

firing. rod: 35 when. thefiring pedal; is: actuated. 7-5; deenergizing-the:solenoids.andzpermittingrplunge ers 20 to pass beneath the respective cam edges I1 under the influence of springs 41. As each successive round is rammed into each gun, the operation is repeated. When more than two guns are present, the operation is the same and is controlled by the slowest gun.

Due to the fact that the important variables are found in the mechanism which operates ahead of the final closing movement of the breechblocks, by synchronizing closing of the blocks substantially completely synchronous fire is obtained. Perfect synchronization is only possible by simultaneous release of the firing pins. As the firing pins are released by the final closing movement of the breechblocks, control of such final closing movement will result in substantial simultaneous release of the firing pins. Any small variation in the strength of the breechblock closing springs in the two guns will not appreciably vary the instant of closing of the blocks, and even this slight variation can be overcome by proper matching of the closing springs. Any such slight variations are not cumulative however.

If it is desired to fire either gun independently, or both guns non-synchronously, the selector switch 3| is moved to the left hand position in Figure 5 to electrically disconnect the circuit 21 and switches 23 from the solenoid circuit so that solenoids l9 will be energized when trigger switch 28 is in closed position.

The synchronizing device embodying the present invention is readily built into a gun mount during manufacture, and is very easily installed on other guns. The side covers l8 need only be provided with openings for plungers 2B, the solenoids l9 and switches 23 are easily attached to the side doors and the wiring may be readily installed. The opening 22 in the breech ring is not necessary as the plungers 20 may be made sufiiciently strong to withstand pressure of roller 2 I, but such opening 22 is desirable to brace the plunger against this pressure.

While I have shown and described the preferred embodiment of the invention, it is to be understood that various changes in the elements and circuits used may be made without departing from the spirit of the invention or the scope of the subjoined claims.

Having thus described my invention, What I claim and desire to protect by Letters Patent is:

1. The combination with a gun installation comprising a plurality of guns adapted for automatic firing, each gun having a breechblock, a breechblock operating member movable to automatically open the breechblock and a firing mechanism operated by movement of the breechblock to fully closed position, of a gun synchronizing device comprising a detent normally in the path of the breechblock operating member of each gun to interrupt the closing movement of each breechblock at a point immediately in advance of its fully closed position, and means to simultaneously withdraw said detents from the paths of the respective breechblock operating members of the guns in response to all breechblocks reaching said point in their closing movements, whereby the breechblocks will complete their closing movements and operate their firing mechanisms in unison.

2. The combination with a gun installation comprising a plurality of guns adapted for automatic firing, each gun having a breechblock, a breechblock operating member movable to automatically open and close the breechblock, and a firing mechanism operated by movement of the breechblock to fully closed position, of a gun synchronizing device comprising a detent normally in the return path of the breechblock operating member of each gun to interrupt the closing movement of the corresponding breechblock at a point immediately in advance of its com-' pletely closed position, and electrically operated means energized by engagement of all said operating members with their respective detents to simultaneously withdraw the detents from the paths of the breechblock operating members of the guns, whereby the breechblocks will complete their closing movements and operate their firing mechanisms in unison, said electrically operated means being actuated by the last breechblock to reach said point in advance of its completely closed position.

3. The combination with a gun installation comprising a plurality of guns adapted for automatic firing, each gun having a breechblock, a breechblock operating member movable to automatically open and close the breechblock, and a firing mechanism operated by movement of the breechblock to fully closed position, of a gun synchronizing device comprising solenoids, each solenoid having a plunger, resilient means urging said plunger into the path of a respective breech operating member of a gun to interrupt the closing movement of each breechblock at a point immediately in advance of its completely closed position, an electrical circuit connecting said solenoids, and a normally open switch associated with each solenoid plunger and closed by lateral pressure of the breech operating member against the plunger, said normally open switches being arranged in a series connection with the solenoid circuit whereby the solenoids will be energized when all of the switches are closed by the breechblock operating members to thereby Withdraw all solenoid plungers simultaneously from the paths of the breechblock operating members to permit all of the breechblocks to complete their closing movements in unison.

4. The combination with a gun installation comprising a plurality of guns adapted for automatic firing, each gun having a breechblock, a-

breechblocir operating member movable to automatically open and close the breechblock, and a firing mechanism operated by movement of the breechblock into fully closed position, of a gun synchronizing device comprising solenoids. a plunger for each solenoid, means normally urging each plunger into the path of the breech operating member of a respective gun to interrupt the closin movement of each breechblock at a point just in advance of its fully closed position, an electrical circuit connecting said solenoids, a normally open switch associated with each solenoid plunger and closed by pressure of the breech operating member against its respective plunger,

said normally open switches being arranged in a series connection with the solenoid circuit whereby the solenoids will be energized only when all of the switches are closed by the breechblock operating members to thereby withdraw all plungers switches from the solenoid circuit to permit non synchronous firing of the guns.

5. The combination with a gun installation comprising a plurality of guns adapted for auto" matic fring, each gun having a breech casing, a breechblock disposed in said casing, a cam operated member to automatically open and close the breechblock, a cam carried by the casing to engage the cam operated member, and a firing mechanism operated by closing of the breechblock, of a gun synchronizing device comprising a solenoid carried by each casing, a plunger for each solenoid, means resiliently urging each plunger to a position adjacent said cam and in the path of the cam operated member to interrupt the closing movement of each breechblock at a point immediately in advance of its completely closed position, an electrical circuit connecting said solenoids, and a normally open switch associated with each solenoid and having an operating member normally engaging the solenoid plunger and adapted to be moved by pressure of the cam operated member against the plunger to close the normally open switch, said normally open switches being arranged in series with the solenoid circuit, whereby the solenoids will be energized when all of the normally open switches are closed by pressure of the cam operated members to thereby simultaneously withdraw all solenoid plungers from the paths of the cam operated members to permit all of the breechblocks to complete their closing movements in unison.

6. The combination with a gun installation comprising a plurality of guns adapted for automatic firing, each gun having a breech casing, a breechblock disposed in said casing, a cam operated member to automatically open and close the breechblock, a cam carried by the casing to engage the cam operated member, and a firing mechanism operated by closing of the breechblock, of a gun synchronizing device comprising a solenoid carried by each casing, a plunger for each solenoid, means resiliently urging said plunger to a position adjacent said cam and in the path of the cam operated member to interrupt the closing movement of each breechblock at a point immediately in advance of its fully closed position, an electrical circuit connecting said solenoids, a normally open switch associated with each solenoid and having an operating member normally engaging the solenoid plunger and adapted to be moved by pressure of the cam operated member against the plunger to close the normally open switch, said normally open switches being arranged in series with the solenoid circuit, whereby the solenoids will be energized when all of the normally open switches are closed by pressure of the cam operated members to thereby simultaneously withdraw all solenoid plungers from the paths of the cam operated members to permit all of the breechblocks to complete their closing movements in unison, and a selector switch disposed in the solenoid circuit and adapted in one position to connect the normally open switches to the solenoid circuit and in another position to disconnect the normally open switches from the solenoid circuit to permit non-synchronous firing of the guns.

7. The combination with a gun mount having a plurality of guns carried thereon and adapted for automatic firing, each gun having a breech casing, a breechblock disposed in said casing, a cam operated member to automatically open and close the breechblock, a cam carried by the casing to operate the cam operated member, and a firing mechanism operated by movement of the breechblock to fully closed position, of a gun synchronizing mechanism comprising solenoids carried by each casing respectively, a plunger for each solenoid, means normally resiliently urging each plunger to a position adjacent said cam and in the path of the cam operated member to interrupt the closing movement of each breechblock at a point immediately in advance of its completely closed position, an electrical circuit connecting said solenoids, a normally open switch associated with each solenoid and having an operating member normally engaging the solenoid plunger and adapted to be moved by lateral pressure of the cam operated member against the plunger to close the normally open switch, said normally open switches being arranged in series with the solenoid circuit, whereby the solenoids will be energized only when all of the normally open switches are closed by pressure of the cam operated members to thereby simultaneously withdraw all of solenoid plungers from the paths of the cam operated members to permit all of the breechblocks to complete their closing movements in unison, and means to automatically open the solenoid circuit when the guns are not in operation.

8. In combination with a pair of guns mounted in side-by-side parallel relation, each gun including a movable breechblock, means operable to so move said breechblock to open and close the same, and firing means operated directly by and in response to the final increment of movement of said breechblock into closed position, retractable plunger means normally interposed in the path of movement of said breechblock operating means to arrest the closing movement of each breechblock at a first position immediately in advance of said final increment of movement, and means to simultaneously retract all said plunger means to thereby render the same ineffective, in response to movement into said first position of that one of said breechblocks last to attain said first position, whereby precise synchronous fire of said gun is attained.

9. The combination recited in claim 8, said retracting means comprising a circuit including a pair of switches in series, and means operated by said final increment of movement of each breechblock into closed position to close a respective switch.

SEYMOUR J. BARR,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,329,668 Trimbach Sept. 14, 1943 2,403,641 Den Ouden .July 9, 1946 2,472,621 Roters July 7, 1949 OTHER REFERENCES War Dept. Manual TM 9-252, April 15, 1942. 

